Angiogenesis, the formation of new blood vessels from existing ones, is essential to many physiological and pathological processes. Normally, angiogenesis is tightly regulated by pro- and anti-angiogenic factors, but in the case of diseases such as cancer, ocular neovascular diseases, arthritis, and psoriasis, the process can go awry. Folkman, J. Nat. Med., 1:27-31 (1995).
There are a number of diseases known to be associated with deregulated or undesired angiogenesis. Such diseases include, but are not limited to, ocular neovascularisation, such as retinopathies, including diabetic retinopathy, age-related macular degeneration, psoriasis, hemangioblastoma, hemangioma, arteriosclerosis, inflammatory disease, such as a rheumatoid or rheumatic inflammatory disease, especially arthritis (including rheumatoid arthritis), or other chronic inflammatory disorders, such as chronic asthma, arterial or post-transplantational atherosclerosis, endometriosis, and neoplastic diseases, for example so-called solid tumors and liquid (or hematopoietic) tumors (such as leukemias and lymphomas). Other diseases associated with undesired angiogenesis will be apparent to those skilled in the art.
Although many signal transduction systems have been implicated in the regulation of angiogenesis, one of the best-characterized and most endothelial cell-selective systems involves the Tie-2 receptor tyrosine kinase (referred to as “Tie-2” or “Tie-2R” (also referred to as “ORK”); murine Tie-2 is also referred to as “tek”) and its ligands, the angiopoietins (Gale, N. W. and Yancopoulos, G. D., Genes Dev. 13:1055-1066 [1999]). There are 4 known angiopoietins; angiopoietin-1 (“Ang-1”) through angiopoietin-4 (“Ang-4”). These angiopoietins are also referred to as “Tie-2 ligands”. (Davis, S., et al., Cell, 87:1161-1169 [1996]; Grosios, K., et al., Cytogenet Cell Genet, 84:118-120 [1999]; Holash, J., et al., Investigative Ophthalmology & Visual Science, 42:1617-1625 [1999]; Koblizek, T. I., et al., Current Biology, 8:529-532 [1998]; Lin, P., et al., Proc Natl Acad Sci USA, 95:8829-8834 [1998]; Maisonpierre, P. C., et al., Science, 277:55-60 [1997]; Papapetropoulos, A., et al., Lab Invest, 79:213-223 [1999]; Sato, T. N., et al., Nature, 375:70-74 [1998]; Shyu, K. G., et al., Circulation, 98:2081-2087 [1998]; Suri, C., et al., Cell, 87:1171-1180 [1996]; Suri, C., et al., Science, 282:468-471 [1998]; Valenzuela, D. M., et al., Proceedings of the National Academy of Sciences of the USA, 96:1904-1909 [1999]; Witzenbichler, B., et al., J Biol Chem, 273:18514-18521 [1998]). Whereas Ang-1 binding to Tie-2 stimulates receptor phosphorylation in cultured endothelial cells, Ang-2 has been observed to both agonize and antagonize Tie-2 receptor phosphorylation (Davis, S., et al., [1996], supra; Maisonpierre, P. C., et al., [1997], supra; Kim, I., J. H. Kim, et al., Oncogene 19(39): 4549-4552 (2000); Teichert-Kuliszewska, K., P. C. Maisonpierre, et al., Cardiovascular Research 49(3): 659-70 (2001)).
The phenotypes of mouse Tie-2 and Ang-1 knockouts are similar and suggest that Ang-1-stimulated Tie-2 phosphorylation mediates remodeling and stabilization of developing vessels in utero through maintenance of endothelial cell-support cell adhesion (Dumont, D. J., et al., Genes & Development, 8:1897-1909 [1994]; Sato, T. N., et al., Nature, 376:70-74 [1995]; Suri, C., et al., [1996], supra). The role of Ang-1 in vessel stabilization is thought to be conserved in the adult, where it is expressed widely and constitutively (Hanahan, D., Science, 277:48-50 [1997]; Zagzag, D., et al., Experimental Neurology, 159:391-400 [1999]). In contrast, Ang-2 expression is primarily limited to sites of vascular remodeling, where it is thought to block Ang-1 function, thereby inducing a state of vascular plasticity conducive to angiogenesis (Hanahan, D., [1997], supra; Holash, J., et al., Science, 284:1994-1998 [1999]; Maisonpierre, P. C., et al., [1997], supra).
Numerous published studies have purportedly demonstrated vessel-selective Ang-2 expression in disease states associated with angiogenesis. These pathological conditions include, for example, psoriasis, macular degeneration, and cancer (Bunone, G., et al., American Journal of Pathology, 155:1967-1976 [1999]; Etoh, T., et al., Cancer Research, 61:2145-2153 [2001]; Hangai, M., et al., Investigative Ophthalmology & Visual Science, 42:1617-1625 [2001]; Holash, J., et al., [1999] supra; Kuroda, K., et al., Journal of Investigative Dermatology, 116:713-720 [2001]; Otani, A., et al., Investigative Ophthalmology & Visual Science, 40:1912-1920 [1999]; Stratmann, A., et al., American Journal of Pathology, 153:1459-1466 [1998]; Tanaka, S., et al., J Clin Invest, 103:34-345 [1999]; Yoshida, Y., et al., International Journal of Oncology, 15:1221-1225 [1999]; Yuan, K., et al., Journal of Periodontal Research, 35:165-171 [2000]; Zagzag, D., et al., [1999] supra). Most of these studies have focused on cancer, in which many tumor types appear to display vascular Ang-2 expression. In contrast with its expression in pathological angiogenesis, Ang-2 expression in normal tissues is extremely limited (Maisonpierre, P. C., et al., [1997], supra; Mezquita, J., et al., Biochemical and Biophysical Research Communications, 260:492-498 [1999]). In the normal adult, the three main sites of angiogenesis are the ovary, placenta, and uterus; these are the primary tissues in normal (i.e., non-cancerous) tissues in which Ang-2 mRNA has been detected.
Certain functional studies suggest that Ang-2 may be involved in tumor angiogenesis. Ahmad et al. (Cancer Res., 61:1255-1259 [2001]) describe Ang-2 over-expression and show that it is purportedly associated with an increase in tumor growth in a mouse xenograft model. See also Etoh et al., supra, and Tanaka et al., supra, wherein data is presented purportedly associating Ang-2 over expression with tumor hypervascularity. However, in contrast, Yu et al. (Am. J. Path., 158:563-570 [2001]) report data to show that overexpression of Ang-2 in Lewis lung carcinoma and TA3 mammary carcinoma cells purportedly prolonged the survival of mice injected with the corresponding transfectants.
In the past few years, various publications have suggested Ang-1, Ang-2 and Tie-2 as a possible target for anti-cancer therapy. For example, U.S. Pat. Nos. 6,166,185, 5,650,490, and 5,814,464 each disclose the concept of anti-Tie-2 ligand antibodies and receptor bodies. U.S. Patent App. Pub. No. 2003/0124129A1 describes certain anti-Ang 2 antibodies and their use in treatment of cancer. Lin et al. (Proc. Natl. Acad. Sci. USA, 95:8829-8834 [1998]) injected an adenovirus expressing soluble Tie-2 into mice; the soluble Tie-2 purportedly decreased the number and size of the tumors developed by the mice. In a related study, Lin et al. (J. Clin. Invest., 100:2072-2078 [1997]) injected a soluble form of Tie-2 into rats; this compound purportedly reduced tumor size in the rats. Siemeister et al. (Cancer Res., 59:3185-3189 [1999]) generated human melanoma cell lines expressing the extracellular domain of Tie-2, injected these cell lines into nude mice, and concluded that soluble Tie-2 purportedly resulted in a “significant inhibition” of tumor growth and tumor angiogenesis.
Hence, an effective anti-Ang-2 therapy might benefit a vast population of cancer patients because most solid tumors require neovascularization to grow beyond 1-2 millimeters in diameter. Such therapy might have wider application in other angiogenesis-associated diseases as well, such as retinopathies, arthritis, and psoriasis.